Carcass traits and organ weights of 10–25-kg body weight Iberian pigs fed diets with different protein-to-energy ratio

Animal Feed Science and Technology 164 (2011) 116–124

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Carcass traits and organ weights of 10–25-kg body weight Iberian pigs fed diets with different protein-to-energy ratio J.A. Conde-Aguilera, M.A. Aguinaga, L. Lara, J.F. Aguilera, R. Nieto ∗ Department of Physiology and Biochemistry of Animal Nutrition, Animal Nutrition Institute (IFNA), Estación Experimental del Zaidín (CSIC), Camino del Jueves s/n, 18100 Armilla, Granada, Spain

a r t i c l e

i n f o

Article history: Received 18 August 2010 Received in revised form 30 November 2010 Accepted 2 December 2010

Keywords: Carcass protein deposition Iberian pigs Organ weights Dietary protein Energy intake

a b s t r a c t Fifty-eight purebred castrated male Iberian (IB) piglets were used to investigate the effects of dietary crude protein concentration (CP, 201, 176, 149 and 123 g CP (kg dry matter (DM)−1 ) and level of feeding (FL, 0.95 and 0.70 × ad libitum) on carcass traits and relative organ weights from 10 to 25 kg body weight (BW). Six piglets were slaughtered at the start of the trial to estimate initial carcass composition. The remaining piglets (n = 52) were randomly assigned to experimental treatments following a factorial design (4 CP × 2 FL) with six or seven piglets per treatment combination. Dietary amino-acid profile (ideal protein) remained constant. Piglets were individually housed (27 ± 1.5 ◦ C) and feed allowance was adjusted weekly. Crude protein and water concentration (g kg−1 ) in the carcasses of piglets slaughtered at 25-kg BW increased linearly as CP was raised (P<0.001). However, no significant differences were observed between diets containing 201 and 176 g CP (kg DM)−1 . Total ash content was also higher as CP increased (P<0.05), whereas crude fat and energy content followed the inverse trend (P<0.001). Protein deposition (PD, g day−1 ) in carcass increased linearly with increasing dietary CP and was maximal in piglets fed diets with 201 and 176 g CP (kg DM)−1 (P<0.001). The effect of dietary CP upon ash and water deposition in carcass was similar as for PD (P<0.001). Fat daily accretion increased linearly with decreasing dietary CP (P<0.001). Average chemical composition of carcass gain was 153, 215, 31 and 602 g kg−1 for CP, crude fat, total ash and water, respectively. Total viscera weight increased by 20% (P<0.001), digestive tract by 25% (P<0.001) and liver and kidneys by 30% (P<0.001) in piglets at the higher FL. Weights of sirloin and ham and total carcass lean (as g (kg carcass)−1 ) increased linearly as CP increased. Lean tissue proportions in shoulder and ham increased and intermuscular dissectable fat in ham decreased as dietary CP was raised. Proportional weights of skin, bone and lean tissue in shoulder and ham increased as FL was reduced (P<0.05) and the opposite trend was found for intermuscular (P<0.05) and subcutaneous (P<0.01) fat in shoulder and intermuscular fat in ham (P<0.01). A diet containing at least 201 g ideal CP (kg DM)−1 (13.7 g ideal CP (MJ metabolisable energy (ME))−1 or 0.99 g total lysine (Lys) (MJ ME)−1 ) provides an adequate CP-to-energy ratio for maximising carcass lean growth in Iberian pigs weighing from 10 to 25 kg BW. © 2010 Elsevier B.V. All rights reserved.

Abbreviations: ADG, average daily gain; IB, Iberian; BW, body weight; CP, crude protein; DM, dry matter; EBW, empty body weight; FL, feeding level; GE, gross energy; HPLC, high-performance liquid chromatography; Lys, lysine; ME, metabolisable energy; N, nitrogen; PD, protein deposition; RW, relative weight. ∗ Corresponding author. Tel.: +34 958 572 757; fax: +34 958 572 753. E-mail address: [email protected] (R. Nieto). 0377-8401/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2010.12.002

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1. Introduction The traditional production system of the Iberian (IB) pig, a native breed raised in the southwest of Spain and Portugal, has relied on outdoor rearing in the Mediterranean forest, particularly at the late stage of fattening. This type of management provides high-quality dry-cured products of relatively high market prices. However, intensification of the production system is broadly practiced during the growing and early fattening stages. In previous articles, we have described the response to different protein and energy intakes in terms of nutrient retention, carcass characteristics and organ development, of growing (15–50 kg body weight (BW); Nieto et al., 2003) and fattening (50–100 kg BW; Barea et al., 2006) IB pigs. These studies underline the lypogenic character of this breed, which has limited carcass lean-tissue deposition and increased deposition of fat, particularly in heavier animals, as compared with conventional pigs of similar BW. Consequently, under intensive management practices, an efficient, sustainable and profitable production of the IB pig can be achieved with diets of lower crude protein (CP)-to-energy ratio than those for conventional pig breeds. Young IB pigs (10–25 kg BW) have greater potential for growth and lean deposition than older IB pigs. Recently, Conde-Aguilera et al. (2010a) observed that the performance of 10–25 kg BW pigs was enhanced with diets containing a minimum of 176 g ideal CP(kg dry matter (DM)−1 or 9.22 g digestible CP (MJ metabolisable energy (ME))−1 , within a range of approximately 120–200 g ideal CP (kg DM)−1 . This dietary CP content is well above the optimal value previously observed by Nieto et al. (2002) in IB pigs weighing from 15 to 50 kg BW (129 g ideal CP (kg DM)−1 , 5.86 g digestible CP (MJ ME)−1 ). These values are, however, lower than the optimal dietary CP-to-energy ratio recommended for conventional breeds (Le Bellego and Noblet, 2002). The aim of the present study was to investigate the effects of dietary CP content and level of feeding, on carcass nutrient deposition, carcass traits and relative weights of organs in Iberian pigs weighing from 10 to 25 kg BW. 2. Materials and methods 2.1. Animals, experimental design and feeding The study was performed with 58 purebred IB barrows taken from 32 litters of six–eight piglets each. Pigs were weaned at 28 days and offered by free choice, a commercial pre-starter diet (222 g CP, 16 g lysine (Lys) (kg DM)−1 ) until the start of the experiment (45 ± 2 days and 9.9 ± 0.09 kg BW). Six piglets were slaughtered at the start of the trial to estimate initial carcass composition. The other 52 piglets were randomly assigned to experimental treatments following a factorial design with four CP (from 200 to 120 g CP (kg DM)−1 ) and two levels of feeding (FL, 0.95 and 0.70 of ad libitum consumption) with six or seven piglets per combination of treatments. Pigs were individually housed in 2 m2 pens located in an environmentally controlled room (27 ± 1.5 ◦ C) and exposed daily to 12 h lighting until slaughter at 25 kg. The experimental diets were isoenergetic and their amino-acid profile (formulated according to the ideal protein concept, British Society of Animal Science, 2003) was maintained constant by diluting the diet with the highest CP concentration, based on barley, soybean meal and fish meal, with a protein-free mixture made of maize starch, cellulose, vegetable oil and a mineral/vitamin premix (Tables 1 and 2). The final CP concentrations were 201, 176, 149 and 123 g (kg DM)−1 , respectively (Table 2). Each diet was offered at the FL described previously in twice-daily equal meals (at 0900 and 1500 h), and water was freely available. Daily feed allowance was adjusted weekly, based on individual BW. Feed refusals were daily collected, dried and weighed to calculate actual feed intakes. The experimental protocol was reviewed and approved by the Bioethical Committee of the Spanish National Research Council (CSIC), Spain, and piglets were cared for following the Spanish Ministry of Agriculture guidelines (Boletín Oficial Estado, 2005). 2.2. Measurements The comparative slaughter technique was used. A digestibility trial was performed at approximately 15 kg BW to determine the total tract apparent digestibility (TTAD) of nutrient and gross energy. Three days before starting excreta collection, the piglets were individually allocated to metabolic cages (0.35 m × 0.80 m) for collection of faeces and urine, separately. Chromic III oxide (Cr2 O3 ) was added to the diet (5 g kg−1 ) at least 5 days before the digestibility measurements started. Uncontaminated faeces and all the urine were collected daily during 5 days. Urine was collected into 50 ml of 4 M H2 SO4 . At the end of the digestibility measurements, composite samples of faeces and urine were obtained separately for the whole period for each pig. The TTAD of dietary nutrients (n) (TTADn; g nutrient n apparently digested (g nutrient n ingested)−1 ) or energy, was calculated as TTADn = 1 − [(Qe × Cr2 O3i )/(Qi × Cr2 O3e )], where e and i indicate faecal excretion and feed intake, respectively, and Q and Cr2 O3 are concentrations of nutrient n and Cr2 O3 in the specified samples. The piglets were slaughtered by exsanguination after electrical stunning at 25 ± 0.5 kg BW. The empty gut, blood, carcass and visceral organs were weighed separately. The head was removed by cutting at the occipito–atlas joint, the feet by cutting at the carpus–metacarpal and tarsus–metatarsal joints and the carcass was divided longitudinally. These components were chilled overnight and weighed. After weighing, they were sealed in plastic bags and kept at −20 ◦ C until analysis. The right half of the carcass was cut into small pieces and ground in a mincer (Talleres Cato, Sabadell, Spain) and homogenised in a cutter (Talleres Cato, Sabadell, Spain), and subsamples were taken for freeze-drying and subsequent analysis. Aliquot samples were analysed for DM, CP, gross energy (GE) and total ash content. Carcass crude fat content was calculated assuming an energy content of 23.85 and 39.75 kJ g−1 for protein and fat, respectively (Wenk et al., 2001). The left half of the carcass was

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Table 1 Ingredient composition and chemical analysis of the diet with the highest protein content (g kg−1 as-fed basis). Ingredients (g kg−1 ) Barley grain Soybean meal, 44% CP Fish meal, 72% CP Dicalcium phosphate Calcium carbonate Common salt Vitamin/mineral pre-mixa l-Lysine HCl, 78.8% l-Threonine, 98% dl-Methionine, 99% l-Tryptophan, 100% Analysed nutrient composition (g kg−1 ) Crude protein Lysine Methionine and cysteine Threonine Tryptophan Isoleucine Leucine Histidine Phenylalanine and tyrosine Valine Crude fat Acid detergent fiberb Dry matter

794.3 130 40 12 8 5 3 5 1.2 0.3 0.2 178.3 12.9 6.5 7.6 2.3 7.1 12.6 4.0 14.3 8.9 22.5 59.1 887

a Provided (per kg of complete diet): retinol, 3.38 mg as retinyl acetate; cholecalciferol, 56.3 ␮g; dl-␣-tocopherol, 25.2 mg as dl-␣-tocopheryl acetate; menadione, 1.5 mg as menadione sodium bisulfite; thiamine, 0.15 mg; riboflavin, 3 mg; pyridoxine, 0.15 mg; cyanocobalamin, 15 ␮g; folic acid, 15 ␮g; nicotinic acid, 22.5 mg; D-pantothenic acid, 15 mg as calcium pantothenate; Mn, 15 mg as MnSO4 ·4H2 O; Fe, 75 mg as FeSO4 ·7H2 O; Zn, 120 mg as ZnO; I, 450 ␮g as KI; Cu, 60 mg as CuSO4 ·5H2 O; Co, 300 ␮g as CoSO4 ·7H2 O. b Calculated based on FEDNA (2003).

dissected as described by García-Valverde et al. (2008). Briefly, midline back-fat measurements were made at first rib, last rib and the last lumbar vertebrae. Carcass length was measured from the proximal end of the first rib to the pubic symphysis. The shoulder was separated from the loin and belly by a straight cut between the second and third ribs and a straight cut 2.5 cm ventral to the ventral edge of the scapula. The ham was removed from the loin by a straight cut between the second and third sacral vertebrae, approximately perpendicular to the shank bones. Each cut retained its corresponding skin and subcutaneous fat. The loin was separated from the belly by a cut beginning just ventral to the ventral side of the scapula at the cranial end and followed the natural curvature of the vertebral column to the ventral edge of the psoas major at the caudal end of the loin. Each cut was weighed. After weighing, the shoulder and ham were separated into skin, subcutaneous fat, intermuscular fat, muscle (including blood vessels, ligaments, tendons and connective tissue) and bone. The empty BW (EBW) was calculated at slaughter as the sum of hot carcass, blood and viscera. Carcass chemical composition at the beginning of the experiment was estimated from the six piglets slaughtered at 10 kg BW, assuming identical composition and EBW-to-BW ratio for the other piglets. Carcass protein, energy, fat and ash retention were then calculated as the difference between the final measured composition of the experimental piglets and the estimated initial composition assessed from the initial group. Table 2 Nutrient composition of the experimental diets. Experimental dieta

High protein dietb (g kg−1 ) Diluting mixturec (g kg−1 ) Analysed composition (dry matter basis) Crude protein (g (kg DM)−1 ) Digestible energy (MJ (kg DM)−1 ) MEd (MJ (kg DM)−1 ) Digestible protein/MEd (g MJ−1 ) Lysine/MEd (g MJ−1 ) a

1

2

3

4

1000 0

875 125

750 250

625 375

176 14.65 14.34 9.22 0.88

149 15.11 14.92 7.87 0.73

123 14.88 14.65 6.14 0.62

201 14.99 14.59 10.80 0.99

Obtained by dilution of the diet with the highest crude protein content with a diluting mixture as specified. See composition in Table 1. Containing (g kg−1 , as fed): maize starch, 873.7; cellulose, 59.1; dicalcium phosphate, 36.7; maize oil (containing butylated hidroxytoluene to provide 0.125 g per kg diluting mixture), 22.5; common salt, 5; vitamin and trace mineral premix, 3. d ME: metabolisable energy. b c

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2.3. Chemical analysis Analyses were performed in duplicate. DM content of feed and freeze-dried carcass and faeces (no. 934.01), total ash (no. 942.05) and total nitrogen (N) in feed and freeze-dried carcass and faecal samples, determined by the Kjeldahl procedure (no. 984.13), were carried out according to the Association of Official Analytical Chemists (AOAC, 2003). Crude protein was determined as total N × 6.25. Chromium III oxide was determined by a micromethod involving alkaline fusion mixture and dry ashing (Aguilera et al., 1988). A DM determination was performed on aliquot samples of freeze-dried materials to establish the residual water content after freeze-drying, and the corresponding analytical result was expressed on a DM basis. Gross energy of feeds and freeze-dried samples of carcass, faeces and urine were measured in an isoperibolic bomb calorimeter (PARR 1356, Biometa, Moline, IL, USA). The latter were freeze-dried in a polyethylene sheet of known energy value and the GE values were obtained by difference. Amino acids in feeds were determined after protein hydrolysis in 6 M HCl plus 1% phenol in sealed, evacuated tubes at 110 ◦ C for 24 h, by high-performance liquid chromatography (HPLC), according to the Waters Pico Tag method (Cohen et al., 1989). Cysteine and methionine were determined as cysteic acid and methionine sulphone, respectively, after oxidation with performic acid before hydrolysis with 6 N HCl (Moore, 1963). Tryptophan was not measured. 2.4. Statistical treatment Data were analysed by two-way analysis of variance (ANOVA) using the GLM procedure of SAS (Statistical Analysis Systems Institute, 2004). The effects of CP, FL and their interactions were included in the statistical model. Piglet was considered as the experimental unit. When interactions between the two main factors were significant, the means for each of the eight treatment combinations were compared by one-way ANOVA. Results are expressed as least-square means and standard error of the mean (SEM). Statistical significance was assessed using Tukey’s t-test. The level of significance was set to 5%. Orthogonal polynomial contrasts were also used to determine linear and quadratic effects of dietary CP on performance, carcass retention variables and growth of body components. 3. Results Piglets did not show any abnormal behaviour or signs of illness during the experiment. Some piglets on the higher FL had feed refusals that were quantitatively recovered and weighed. Main data regarding growth performance are shown in Table 3. Daily ME intake for the entire experimental period was not affected by dietary CP concentration (11.93 and 8.55 MJ ME day−1 for the high and low FL assayed, respectively). Average daily gain (ADG) increased linearly with increases in dietary CP (P<0.001). Piglets fed the 201 and 176 g CP (kg DM)−1 diets had increased ADG as compared with those fed the two lower CP diets (340 g day−1 vs. 301 g day−1 ; P<0.001). The rate of growth was highest in piglets fed close to ad libitum consumption (P<0.001). Gain:feed ratio improved with increasing CP concentration and was higher for pigs fed close to ad libitum consumption than for restricted pigs (P<0.001). No CP × FL interactions were observed. 3.1. Carcass deposition of nutrients The average chemical composition of the carcass of piglets slaughtered at the start of the experiment was (g kg−1 ) 155 (SEM 2.4), 113 (SEM 5.1), 691 (SEM 3.9), 40.8 (SEM 1.97) and 8.19 MJ kg−1 (SEM 0.159) for CP, crude fat, water, total ash and energy, respectively. CP and water concentration (g kg−1 ) of the carcasses of piglets slaughtered at the end of the experiment (25 kg BW) increased linearly as dietary CP was raised (P<0.001). However, no significant differences were observed between diets containing 201 and 176 g CP (kg DM)−1 (Table 4). Total ash content was also higher in piglets fed diets of higher CP (P<0.05); however, crude fat and energy content followed an inverse trend, increasing linearly as dietary CP decreased Table 3 Effects of crude protein content (CP, g (kg dry matter)−1 ) of the diet and level of feeding (FL, ×ad libitum consumption) on growth performance of Iberian piglets from 10 to 25 kg body weight. CP

MEb intake ADGc , d Gain:feedd

FL

P-value

201

176

149

123

S.E.M.

0.95

0.70

S.E.M.

CP

FL

CP × FL

10.17 344a 0.496a

10.04 336a 0.481a

10.54 310b 0.438b

10.22 292b 0.416b

0.217 8.9 0.0079

11.93 391 0.488

8.55 251 0.426

0.153 6.3 0.0056

NS

***

***

***

***

***

NS NS NS

a

Values with the same letter are not significantly (NS) different (NS = P>0.05). a n = 6 or 7 piglets per each CP × FL combination. b ME: metabolisable energy (MJ day−1 ). c Average daily gain (g). d Linear effect of CP (P<0.001). *** Probability of significance: P<0.001.

a

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Table 4 Effects of crude protein content (CP, g (kg dry matter)−1 ) of the diet and level of feeding (FL, ×ad libitum consumption) on carcass composition and carcass nutrient deposition of Iberian piglets slaughtered at 25 kg body weight. CP

Carcass composition (g kg−1 ) Crude proteinb Crude fatb Total ash Waterb Energyb (MJ kg−1 ) Carcass gainb (g day−1 ) Nutrient deposition Proteinb (g day−1 ) PD/PIc (g g−1 ) PD:MEb , c intake (g MJ−1 ) Fatb (g d−1 ) Ashb (g day−1 ) Waterb (g day−1 ) Total energyd (MJ day−1 )

FL

P-value

201

176

149

123

S.E.M.

0.95

0.70

S.E.M.

CP

FL

CP × FL

163a 190c 35.4ab 611a 11.5c 229a

160a 199c 37.0a 604a 11.7c 227a

152b 234b 33.8b 580b 12.9b 212ab

144c 266a 33.8b 556c 14.0a 198b

1.9 6.1 0.91 4.8 0.21 5.8

150 228 33.5 588 12.4 253

160 216 36.5 587 12.6 180

1.4 4.3 0.6 3.3 0.150 4.3

***

***

***

#

**

***

NS NS NS NS NS NS

36.7a 0.260 3.59a 49.0c 6.87ab 143a 2.82

34.8a 0.283 3.48a 52.4bc 7.21a 140a 2.91

29.6b 0.282 2.83b 60.6ab 5.78bc 122b 3.12

25.1c 0.292 2.46b 65.4a 5.31c 106c 3.20

1.11 0.0090 0.101 2.6 0.325 3.9 0.111

35.3 0.274 2.98 68.7 6.85 149 3.57

27.7 0.285 3.20 45.0 5.72 106 2.45

0.78 0.0064 0.072 1.9 0.230 2.8 0.079

***

***

NS

NS

a

a

*

**

***

NS NS

***

*

***

***

***

***

**

***

***

#

***

NS NS NS NS NS NS NS

Values with the same letter are not significantly (NS) different (NS = P>0.05). a n = 6 or 7 piglets per each CP × FL combination. b Linear effect of CP (P<0.001). c PD: protein deposited, PI: protein intake, ME: metabolisable energy. d Linear effect of CP (P<0.05). * Probability of significance: P<0.05. ** Probability of significance: P<0.01. *** Probability of significance: P<0.001. # Probability of significance: 0.05
(P<0.001). Restricted-fed piglets had greater CP (P<0.001) and total ash (P<0.01) and tended to have lower (P=0.06) crude fat carcass contents than those on the higher FL. No significant effect of FL was detected on water and energy contents. No CP × FL interactions were detected. Carcass total gain (Table 4) increased linearly with increasing dietary CP (P<0.01). However, piglets fed diets with 201 and 176 g CP (kg DM)−1 had similar gain (228 g day−1 ). The ADG was greater in piglets fed close to ad libitum consumption than in restricted pigs (253 g day−1 vs. 180 g day−1 ; P<0.001). Carcass gain and ADG were linearly correlated (P<0.001) and the carcass daily gain accounted for 57.2% of whole-body gain. The equation found was as follows: Carcass gain (g day−1 ) = 30 (SEM 6.7) + 0.572 (SEM 0.0202) × ADG (g day−1 )

(n = 52; R2 = 0.95)

PD (g day−1 ) in the carcass of piglets fed diets of 149 and 123 g CP (kg DM)−1 was lower than in those fed 201 and 176 g CP (kg DM)−1 , with no significant differences between these two last treatments (P<0.001). The effect of dietary CP on carcass PD was linear (P<0.001). The efficiency of carcass PD, expressed as the ratio PD:CP intake (g g−1 ) was not significantly altered by dietary CP. However, the ratio carcass PD:ME intake (g MJ−1 ) was 34% higher in diets with 201 and 176 g CP (kg DM)−1 than in diets of lower CP (P<0.001). The rates of carcass PD and whole-body PD were related by linear regression: Carcass PD (g day−1 )=1.64 (SEM 0.854)+0.680 (SEM 0.0188) × whole-body PD (g day−1 )

(n = 52; R2 =0.97)

The resulting equation shows that 68.0% of total daily PD occurred in the carcass of the IB piglet growing from 10 to 25 kg BW. The effect of CP upon carcass ash and water deposition was similar to that for PD (P<0.001). Carcass fat daily accretion (P<0.001) and energy deposition (P<0.05) increased linearly with decreasing dietary CP. The rates of deposition of nutrients and energy were greater in the carcasses of piglets on the higher FL than in those on the lowest feed allowance (27% for CP, 53% for crude fat, 20% for ash, 40% for water and 46% for energy retention, respectively; P<0.01, Table 4). The carcass PD:ME intake ratio (g MJ−1 ) was higher in piglets fed for 0.70 of ad libitum consumption than in those receiving the highest feed allowance. No significant CP × FL interactions were detected. Expressed on an energy basis, the average carcass protein and fat deposition of piglets fed the diets containing 201 and 176 g CP (kg DM)−1 accounted for 0.303 (SEM 0.0103) and 0.697 (SEM 0.0103) of total energy retained, respectively. The average chemical composition of 1 kg carcass gain was 153, 215, 31 and 602 g of CP, crude fat, total ash and water, respectively. The mean energy content of carcass gain was 12.54 kJ g−1 .

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Table 5 Effects of crude protein content (CP, g (kg dry matter)−1 ) of the diet and level of feeding (FL, ×ad libitum consumption) on relative organ weights (RW, g (kg empty BW)−1 ) and carcass traits of Iberian piglets slaughtered at 25 kg body weight (BW). CP

RW Carcass Head Head, feet and tail Total viscera Digestive tract Liver Kidneysb Heart Blood Carcass length (cm) Backfat thickness (cm) First rib Last rib Last lumbar RWc Sirloinb Butt lean Loin Ribs Spine Backfat Shoulderd Hamd Kidney fatb Belly Carcass leand , e

FL

P-value

201

176

149

123

S.E.M.

0.95

0.70

S.E.M.

CP

FL

CP × FL

671 90.2 115 146 66.2 28.6 4.72a 4.98 59.1 50.0

672 91.4 117 145 66.0 27.1 4.72a 5.28 58.8 50.5

679 92.4 118 141 63.9 26.4 4.27ab 5.25 54.9 51.1

674 93.5 119 144 63.2 26.6 3.96b 5.13 55.3 50.6

4.3 2.06 2.2 3.6 1.47 0.77 0.188 0.128 1.48 0.56

667 87.2 112 157 72.1 30.7 4.97 5.28 57.7 49.7

681 96.5 123 131 57.5 23.6 3.87 5.04 56.4 51.4

3.1 1.45 1.6 2.5 1.04 0.54 0.133 0.090 1.05 0.39

NS NS NS NS NS NS

**

NS NS NS NS NS NS NS

a

a

*** *** *** *** ***

*

***

NS

#

*

#

NS

NS

**

NS NS

1.87 1.38 1.36

2.23 1.20 1.18

2.31 1.39 1.29

2.43 1.32 1.25

0.176 0.123 0.130

2.36 1.22 1.16

2.05 1.43 1.38

0.125 0.087 0.092

NS NS NS

NS NS

0.85a 3.85 4.98 7.43 6.55 3.42 24.7 34.7a 0.97b 12.6 43.9a

0.79a 4.65 4.60 7.52 6.85 3.48 25.3 33.3ab 1.10ab 12.4 42.9a

0.74ab 4.32 4.80 7.11 6.44 3.86 25.7 33.3ab 1.26ab 12.5 38.4b

0.64b 4.48 4.30 7.65 6.59 3.76 25.5 33.2b 1.43a 12.5 39.8ab

0.039 0.239 0.232 0.183 0.407 0.147 0.27 0.40 0.094 0.28 1.51

0.71 4.52 4.35 7.62 6.77 3.44 25.7 32.9 1.30 12.7 40.7

0.80 4.12 5.00 7.23 6.44 3.82 25.0 34.3 1.07 12.2 41.8

0.028 0.169 0.164 0.129 0.288 0.104 0.19 0.28 0.066 0.20 1.07

**

*

NS NS NS NS NS

NS

*

** *

NS

NS NS NS NS NS NS 0.06 NS

*

*

#

*

*

***

NS NS NS NS NS

**

*

NS

#

*

NS

Values with the same letter are not significantly (NS) different (NS = P>0.05). a n = 6 or 7 piglets per each CP × FL combination. b Linear effect of CP (P<0.01). c g (kg carcass without head)−1 . d Linear effect of CP (P<0.05). e Sum of: sirloin, butt lean, loin and lean tissue of shoulder and ham. * Probability of significance: P<0.05. ** Probability of significance: P<0.01. *** Probability of significance: P<0.001. # Probability of significance: 0.05
3.2. Carcass traits and organ weights Dietary CP did not have any significant effect on the relative weights (RWs) of carcass, viscera and other whole-body components (g (kg EBW)−1 ), except for the RW of kidneys, which increased as CP increased (P<0.05; Table 5). On the other hand, the FL regime had a significant effect on RW of all body components, except blood. The weight of carcass decreased (P<0.01) and that of head (P<0.001) was reduced approximately by 9%, in piglets fed close to ad libitum consumption with respect to more restricted piglets. By contrast, the RW of total viscera, digestive tract, and liver and kidneys increased by 20%, 25% and 30%, respectively, in piglets fed for 0.95 of ad libitum consumption as compared with piglets on the lowest feed intake (P<0.001). Midline backfat thickness measurements were not affected by dietary CP (Table 5). Backfat thickness tended to increase at the first rib (P=0.09) and decreased at the last lumbar vertebrae (P<0.05) with increasing FL. The RW of sirloin and ham (g (kg carcass without head)−1 ) increased as dietary CP increased (P<0.01 and P<0.05, respectively). Total carcass lean increased by 11% in piglets fed diets containing 201 and 176 g CP (kg DM)−1 (P<0.05). Kidney fat increased progressively with decreasing dietary CP (P<0.01). As a result of feed restriction, the RW of sirloin (P<0.05), loin (P<0.05) and ham (P<0.001) increased, whereas the weight of ribs, shoulder and kidney fat (P<0.05) was reduced. The RW of the belly also tended to be reduced (P=0.078) in restricted piglets. There were no significant CP × FL interactions for any trait except for RW of heart (P=0.016) and backfat (P=0.016). 3.3. Shoulder and ham dissection The RW of lean tissue in shoulder (P<0.001) and ham (P<0.01) increased linearly as the CP was raised (Table 6). The RW of bone in shoulder and ham was not affected by dietary CP and that of skin in shoulder showed a tendency to increase as

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Table 6 Effects of crude protein content (CP, g (kg dry matter)−1 ) of the diet and level of feeding (FL, ×ad libitum consumption) on relative weight of tissues (g kg−1 ) in shoulder and ham of Iberian piglets slaughtered at 25 kg body weight. CP

Shoulder Skinb Bone Leanc Intermuscular fatb Subcutaneous fatc Ham Skin Bone Leanc Intermuscular fatc Subcutaneous fatc

FL

201

176

149

123

73.8 173.6 536.4a 52.3 164.0b

75.4 174.4 522.7a 57.8 169.6b

72.4 171.8 504.3ab 61.0 190.5b

70.1 174.2 470.3b 61.4 224.0a

61.2 157.4 604.5a 48.7c 128.2

60.7 164.6 589.3ab 51.5bc 133.9

59.8 170.9 549.4b 64.6a 155.2

54.6 167.5 554.5ab 62.0ab 161.5

a

S.E.M.

P-value a

0.95

0.70

S.E.M.

1.38 3.04 9.77 2.77 7.54

71.2 169.6 498.4 61.9 198.9

74.7 177.3 518.5 54.4 175.1

0.98 2.15 6.91 1.96 5.33

2.34 5.75 14.15 2.79 7.38

58.6 169.1 557.4 61.2 153.8

59.5 161.2 591.5 52.2 135.6

1.65 4.07 10.01 1.97 5.22

FL

CP × FL

#

*

NS

*

***

*

#

*

***

**

NS NS NS NS NS

NS NS

NS NS

*

*

***

**

**

*

CP

NS NS NS NS *

Values with the same letter are not significantly (NS) different (NS = P>0.05). a n = 6 or 7 piglets per each CP × FL combination. b Linear effect of CP (P<0.05). c Linear effect of CP (P<0.001). * Probability of significance: P<0.05. ** Probability of significance: P<0.01. *** Probability of significance: P<0.001. # Probability of significance: 0.05
CP was elevated (P=0.06). Shoulder subcutaneous fat increased linearly as CP decreased, achieving a maximum (224 g kg−1 ; P<0.001) in piglets fed the diet supplying 123 g CP (kg DM)−1 . A similar trend was observed for shoulder intermuscular fat (P=0.09). Intermuscular dissectable fat in ham increased linearly (P<0.001) with decreasing dietary CP. The FL regime had a significant effect on most of the dissectable components of shoulder and ham, except for skin and bone proportions in ham. The RW of skin, bone and lean tissue in shoulder increased as feed intake was reduced (P<0.05), and the opposite trend was found for intermuscular and subcutaneous fat in shoulder (P<0.05 and P<0.01, respectively) and intermuscular fat in ham (P<0.01). No significant CP × FL interactions were observed for dissectable components of shoulder and ham, except for the RW of subcutaneous fat tissue in ham (P<0.05). When the data were analysed by one-way ANOVA, the subcutaneous fat of ham from piglets on the highest FL was higher than that of the more restricted pigs only when fed the diets containing 149 and 123 g CP (kg DM)−1 (P<0.01; data not shown). 4. Discussion One of the main factors affecting body composition and growth is pig genotype. At the same physiological age, selected pigs have a higher capacity for lean deposition and lower lipid deposition rate than unimproved pigs (van Lunen and Cole, 1996). Consequently, carcass gain and composition differ, and, therefore, protein and energy requirements vary widely between pig genotypes. Nieto et al. (2002) and Barea et al. (2007) have shown that protein requirements of growing and fattening IB pigs are considerably lower than those reported for conventional lean pigs at similar stages of growth. These authors observed also that the maintenance energy requirements of IB pigs were 6–10% lower than those of lean pigs, probably associated with their relatively smaller lean mass. In the present work, growth performance was enhanced with diets that contained 201 and 176 g CP (kg DM)−1 , equivalent to 10.8 and 9.22 g digestible protein (MJ ME)−1 . Nieto et al. (2002) reported that at a later stage of growth (15–50 kg BW), the IB pigs require only 130 g ideal CP (kg DM)−1 (5.86 g digestible CP (MJ ME)−1 ) for optimal growth. These results suggest a considerable decrease in growth potential of the weaned IB piglet with age. This is not surprising as it is known that the potential for PD decreases as the pig approaches maturity (van Lunen and Cole, 1996). Average ME intakes were 11.93 and 8.55 MJ day−1 (1478 and 1056 kJ kg0.75 day−1 , for piglets fed at 0.95 and 0.70 of ad libitum consumption). Nieto et al. (2002) estimated that the ME requirements for maintenance of IB pigs growing from 15 to 50 kg BW was 422 kJ kg0.75 day−1 . Therefore, pigs in the current experiment consumed approximately 3.5–2.5-fold their ME maintenance requirements. Nieto et al. (2002) reported in IB growing pigs (15–50 kg BW) fed diets close to ad libitum consumption feed conversion ratio (FCR) 35% lower than those found in present experiments (0.488 vs. 0.313). Nevertheless, the growth rate of the IB piglet is rather moderate compared with modern piglets of a similar BW range fed diets with optimal CP (Lys)-to-energy ratio (van Lunen and Cole, 1996; Le Bellego and Noblet, 2002; Urynek and Buraczewska, 2003; Kendall et al., 2008). Carcass protein content of IB piglets fed diets supplying 201 and 176 g CP (kg DM)−1 was in the lower range of the values (160–176 g protein (kg carcass)−1 , 18.7–25 kg BW) reported for conventional or modern piglets of similar BW (Shields et al., 1983; Thomke et al., 1995; Dritz et al., 1996; Owen et al., 2001; Conde-Aguilera et al., 2010b). Further, values of water content were 7–13% lower, total ash was in the upper range and crude fat content was clearly above (50–100 g more crude fat (kg carcass)−1 ) those reported in the cited articles. In fact, carcass water-to-protein ratio ranged from 3.7 to 3.9, a value

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somewhat higher than those previously found by Nieto et al. (2003) in growing IB pigs (3.5–3.6) and slightly below ratios (3.9–4.3) derived from experiments with conventional or modern piglets (Shields et al., 1983; Thomke et al., 1995; Dritz et al., 1996; Owen et al., 2001; Conde-Aguilera et al., 2010b). Obviously, carcass composition at slaughter was heavily influenced by daily protein and fat deposition, which, in piglets fed diets with 201 and 176 g CP (kg DM)−1 at 0.95 of ad libitum intake, averaged 40.3 and 60.6 g day−1 for CP and crude fat, respectively. The crude fat:CP ratio in carcass daily gain was 1.5, considerably greater than values of 0.56–0.88 reported for conventional piglets by Dritz et al. (1996), Owen et al. (2001) and Trindade Neto et al. (2004). These figures highlight the lipogenic profile of the IB pig breed, even during the early growth stages. In contrast to IB pigs weighing from 15 to 50 kg BW, in which protein and fat carcass contents remained fairly constant through a wide range of dietary CP (101–223 g CP (kg DM)−1 ; Nieto et al., 2003), carcass protein content and carcass daily PD in younger IB piglets was considerably reduced when fed diets with suboptimal CP content. The reduction in protein accretion was accompanied by a noticeable increase in carcass fat deposition (15–20%), indicating that the young IB piglet was more sensitive to protein restriction than the older IB pig. Therefore, adequate dietary CP-to-energy ratios are essential for optimal piglet lean growth. The highest carcass PD, obtained when piglets were fed close to ad libitum consumption diets of 201 and 176 g CP (kg DM)−1 , averaged 40.3 g day−1 , a value which is consistent with that previously reported for growing IB pigs weighing from 15 to 50 kg BW (54.6 g day−1 ) fed at 0.95 of ad libitum consumption a diet containing 129 g crude (ideal) protein (kg DM)−1 (Nieto et al., 2003). Further, Barea et al. (2006) studying fattening IB pigs from 50 to 100 kg BW reported 55.7 g day−1 when fed at 0.95 of ad libitum consumption a diet containing 95 g crude (ideal) protein (kg DM)−1 . However, in the present experiments, although differences in PD of piglets receiving the two highest CP diets were small and not significant, the linearity of the effect of dietary CP on PD suggests that the maximal potential for protein accretion might have not been reached. In all cases, carcass protein was more efficiently deposited in the young IB piglet (3.54 g protein (MJ ME)−1 vs. 2.12 g protein (MJ ME)−1 and 1.15 g protein (MJ ME)−1 intake, respectively). On the other hand, carcass fat gain averaged 52, 157 and 355 g day−1 for IB pigs weighing from 10 to 25 kg BW (current trial), 15 to 50 kg BW (Nieto et al., 2003) and 50 to 100 kg BW (Barea et al., 2006), respectively. These data support the hypothesis that the IB pig reaches maturity rather early and underline the limited capacity for carcass lean growth of this pig breed. Except for the kidneys, the RW of visceral organs were not affected by changes in dietary CP, in agreement with data of Le Bellego and Noblet (2002) in conventional piglets fed diets with CP varying from 169 to 224 g kg−1 . However, in conventional growing pigs, the excess of protein supply seems to be associated with increased visceral organs mass (Le Bellego et al., 2002). Nieto et al. (2003) observed also increased weight of the digestive tract tissues in growing IB pigs fed diets with excess of CP. Similarly, Nieto et al. (2003) and Barea et al. (2006) have recorded higher RWs of kidneys in growing and fattening IB pigs as dietary CP was increased, probably because of higher metabolic activity associated with urea synthesis and excretion. For IB piglets fed close to ad libitum consumption, the average proportion of total visceral mass was 157 g (kg EBW)−1 , a value considerably higher than those found in growing (127 g (kg EBW)−1 , Nieto et al., 2003), fattening (102 g (kg EBW)−1 , Barea et al., 2006) and finishing (97 g (kg EBW)−1 , García-Valverde et al., 2008) IB pigs under similar feeding conditions. This reduction in visceral mass with age has been associated with increasing maturity (Kolstad and Vangen, 1996). In the present work, raising FL resulted in increases in the RW of total viscera, digestive tract, liver and kidneys, as has been previously described for pigs of lean and obese genetic types at different stages of growth (Koong et al., 1983; Rao and McCracken, 1992; Nieto et al., 2003; Barea et al., 2006). An increased RW of visceral tissues might affect the proportion of ME intake required for maintenance of body functions because visceral tissues are metabolically more active than carcass tissues (Rivera-Ferre et al., 2005). We have not found any research in the literature on the effect of dietary CP on RWs of carcass components of piglets, although some data are available for pigs close to market weights. For example, Wagner et al. (1999) studied changes in body composition in barrows and gilts of five genetic lines and weighing from 25 to 152 kg BW. At 25 kg BW, pigs fed freechoice diets formulated to allow maximal protein accretion had longer carcasses (3.4–3.7 cm longer) with 9% greater lean proportion and 35% lower last-rib backfat thickness than the piglets of the current experiment. Compared with IB pigs from 15 to 50 kg BW, the RWs of carcass lean components of the piglets from the present experiment were more sensitive to changes in dietary CP or FL. For example, sirloin, ham and total carcass lean proportion increased with increasing CP. In heavier growing pigs, only sirloin proportion increased as dietary CP was augmented from marginal to adequate levels (Nieto et al., 2003). Increasing dietary CP increased lean proportions in shoulder and ham of piglets similarly as reported for ham lean proportions in growing pigs (Nieto et al., 2003). Carcass length and proportion of lean components (except for shoulder) were greater in restricted-fed pigs than in animals fed close to ad libitum consumption. The effect of reducing feed intake was more pronounced in IB piglets than in growing pigs (Nieto et al., 2003), resulting in increased proportions of lean tissue in shoulder and ham, and a general decrease of fat depots. A reduction in ME intake led to leaner carcasses as a result of the increased proportion of ME above maintenance used for PD (van Milgen et al., 2000). Nevertheless, this feeding strategy will decrease PD, and, therefore, will increase the time required to reach a certain BW. 5. Conclusions The pattern of carcass nutrient deposition and the peculiarities of composition of carcass and non-carcass components in IB pigs weighing from 10 to 25 kg BW suggest the convenience of applying a specific protein-to-energy regime that is

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clearly differentiated from those recommended for older IB pigs or for more selected piglets of the same age. According to the results obtained in the present work, a diet containing at least 201 g ideal CP (kg DM)−1 (13.7 g ideal CP (MJ ME)−1 or 0.99 g total Lys (MJ ME)−1 ) provided to allow ad libitum consumption will satisfy the protein requirement for maximising carcass lean growth at this stage of growth. Acknowledgements Supported by the Spanish Ministry of Science and Innovation (MICINN, grant No. AGL2005-1652). J.A. Conde-Aguilera ˜ was recipient of a FPI grant from MCINN. Thanks to M.A. Linán, A. Rodríguez, L. González, J.M. Rodríguez and F. Funes for their skilful assistance. Further, we are very grateful to Sánchez Romero Carvajal Jabugo S.A. (Seville, Spain) for the provision of piglets. References Aguilera, J.F., Prieto, C., Molina, E., Lachica, M., 1988. A micromethod for routine determination of chromic oxide in nutrition studies. Analysis 16, 454–457. 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